Compared a Thin Film Transistor Liquid Crystal Display (TFT LCD) with a Twisted-Nematic (TN) LCD or a Supertwisted-Nematic (STN) LCD, a TFT LCD is active driving so it has merits like good image quality, and quick response time. Therefore, TFT LCDs become the main fashion of LCDs gradually.
However, normally there are at least five steps of mask in the manufacturing process for a TFT array substrate so the manufacturing cost of an array substrate is higher than a traditional passive-matrix LCD.
Accordingly, people started to develop that using Metal-Insulator-Metal (MIM) thin film diodes to substitute TFTs. The thin film diode technology is developed by Seiko and Epson companies, which is specially used for display of mobile phones. Thin film diode is a compromise between TFT and STN. The brightness and the color saturation between thin film diode are better than STN's , and saves more power than TFT. The main characteristic is that thin film diode serves high image quality and the display easy to watch no matter under the condition of backlight-on (transmission mode) or backlight-off (reflect mode), and thin film diode has merits of low power consumption, high image quality, and quick response time.
A traditional MIM LCD does not need a storage capacitor. Every pixel only uses the liquid crystal capacitor of the pixel to be the storage device for data write-in such that the active matrix LCDs can be completed. Compared with the manufacturing process for TFTs, the manufacturing process for MIMs only needs 2˜3 steps of masks and hence it has a very clear advantage of cost.
However, a traditional MIM LCD has the problems of image residual and not easy to control the gray scale. Accordingly, U.S. Pat. No. 6,222,596 disclosed a symmetrical MIM diodes arrangement in every utilized pixel. The method of using two scan lines to drive one pixel solves the problems of image residual and not easy to control the gray scale for a traditional MIM LCD.
In U.S. Pat. No. 6,222,596, every pixel structure of every row of pixels is shown in FIG. 1. Each pixel includes a common electrode 9, a pixel electrode 8, a liquid crystal layer 7 between the two electrodes of the common electrode 9, two sets of MIM diodes 10, 11 that are symmetrical to a connection point 12, a data line that connects to the common electrode 9, and the select lines 21 and 22 that respectively connect to the sets of MIM diodes 10, 11.
Every pixel of U.S. Pat. No. 6,222,596 has symmetrical MIM diodes, and each pixel is composed of a pair of select lines 21, 22 and a single data line 31. Due to the restriction of this design rule, the method of driving one pixel by a pair of select lines 21, 22 that used by U.S. Pat. No. 6,222,596 will reduce the effective emitting area (aperture rate) of each pixel relatively. Moreover, the following manufacturing process for IC bonding becomes a big problem because the quantity of whole channel increased. More ICs are needed to control all circuits, and larger area is needed such that there is enough space to design the control circuit. As a result, not only the circuit design becomes more complicated that affects the yield rates but also the needed IC parts are increased that increase the manufacturing cost.